A traditionally successful approach to viral vaccines, whole inactivated virus (WIV), has received relatively little attention in the overall effort to develop an effective HIV/AIDS vaccine. Only one inactivated virus product (the Salk/IRC Immunogen) has been tested in humans and this product is envelope depleted and has been tested only as a therapeutic rather than a prophylactic immunogen. Since major target epitopes for antibody neutralization are in the envelope glycoprotein, it is generally considered a desirable component of a prophylactic immunogen. Thus far, however, immunization of humans with monomeric recombinant envelope glycoprotein has resulted in relatively type-specific neutralization and very little neutralization of primary isolates. The few monoclonal antibodies that demonstrate broad primary- isolate neutralization generally recognize conformation dependent epitopes. Such epitopes might be retained on whole inactivated virions. Photochemical treatment (PCT) with psoralen and UV light is a promising approach to inactivating HIV without disrupting "native" oligomeric structures. We propose to investigate a potentially scaleable process using a proprietary variant of psoralen (5-59) that lacks the in vitro mutagenicity associated with conventional psoralen methods. In addition, 5-59 inactivated products have undergone extensive safety testing in humans. The objectives of this study will be l) to investigate methods to produce and concentrate pilot-scale preparations of HIV with minimal envelope loss, 2) to confirm and Optimize a photochemical treatment process, which will use the novel psoralen 5-59, and UVA to inactivate HIV to an acceptable level while retaining gpl20 and its conformational epitopes, 3) to design/construct a novel flow PCT that is capable of treating laboratory scale quantities (5 L) of HIV culture and is capable of being scaled-up to treat production scale quantities (5000 L), 4) investigate and identify potential process steps that can be used to reduce levels of residual psoralen while maintaining native gp120 structure, 5) investigate potential interactions between PCT and other inactivation processes and determine an optimal process sequence and conditions for obtaining a double- inactivated WIV with intact gpl20, and 6) investigate animal immunogenicity of these preparations.